In a situation wherein backhaul and access radio interfaces are co-located and/or in the same radio band, it is difficult to isolate the interfaces to avoid or prevent cross-interference with each other without bulky, expensive, and power-hungry filters and amplifiers.
Typically, a guard band is an intentionally unused part of the radio spectrum between two radio bands, or on either side of a single designated radio band, left unused for the purpose of preventing interference. By separating two wider frequency ranges, guard bands help to ensure that both can transmit simultaneously without interfering with each other. Typically, in order to ensure that certain frequencies are not used, filters are required.
LTE has built-in guard bands between designated bands. In LTE, guard bands of 1 MHz on either side of a designated band are common. As LTE is sensitive to interference, rigorous filtering is required for these guard bands, which requires high-performance and expensive filters.
Fractional frequency reuse (FFR) and/or inter-cell interference coordination (ICIC) are techniques used in wireless networks for reducing interference. In particular, interference is reduced for users at the edge of a base station's coverage region (called cell edge users). As implied by the name of the technique, interference in a given cell is reduced by coordination of potentially interfering transmissions from a base station in another cell.